BRACHYUEA. 375 



Individual. The rostrum is stouter, more swollen and more clumsy in Trigonothir 

 than in Simocarcinus simplex (includes S. pyramidatus) and S. camelus, but it is 

 essentially the same otherwise. In all these its under surface is flattened proxhnally, 

 while distallv it is concave and produced into lateral carina?: and its apex tends to 

 he threedobed, the lobes set at angles of 120 (very approximately) to each other. 1 

 have seen no specimens of Simocarcinus with the laterally compressed acute rostrum 

 given by Miers as a generic character. Klunzinger (p. 18) revises Miers' definition of 

 Trigonothir, transferring to it the species pyramidatus. As a new generic character 

 iie gives the absence of hepatic lobes in the female. The evidence of the present 

 specimens confirms me in doubting the validity of this. As another new generic 

 distinction he points out that in Trigonothir the chelipeds of the adult male are 

 unequal. With the additional evidence available to me, I would suggest that this 

 inetpiality observed only in a single example (Klunzinger, pi. i., fig. 3) is due 

 t<> regeneration. I unite Simocarcinus and Trigonothir under the name of the former 

 and for the present distinguish this genus from Huenia by two characters : 



(1) Pre-ocular spine. This is present in Huenia, absent in Simocarcinus. 

 (2) Rostrum. In Huenia this is sharp-edged below and has an acute tip; in 

 Simocarcinus it has a flattened under surface which tends to be concave distally, 

 where its lateral edges are produced the tip of the rostrum tends to be trilobed. 



Mensethius monoceros (Latreille), 1825 A.l, p. 197. 

 Localities: Cheval Paar, Gulf of Manaar, seven specimens (A, /, g, &c.) ; Aripu 

 coral reefs, ten specimens (c, a, e, i, &c); off Mutwal Islaud, eight specimens (j) : 

 Jokkenpiddi Paar. two specimens (b, d); Navakaddu Paar, one specimen. 



Description : 



Males. (a). (b). (c). (</). (-). 



C.l. . . . 6-00 7-00 7-50 9-25 9"50 



R.L-S-C.L. 0-58 0-50 0-37 0"49 0*55 



Ovig. females. (/,). (/). (m). () 



C.l 975 975 975 10-25 



R.L-S-C.L 0-32 0-49 0-51 (V59 



The first three of the above males are young ; there is evidence in the collection 

 that this is a species showing facultative dimorphism. 



The specimens show considerable variation in number of tubercles on dorsal surface 

 of the carapace and in the teeth of the lateral border. The majority resemble the 

 variety figured by Dana as Menosthius sub-sen'atus rather than any other variety. 

 Some tend to combine the characters of two or more of Dana's figures, e.g., of the 

 three specimens from Cheval Paar, one agrees fairly with the figure of M, sub- 

 serratus, while the other two agree with this figure in character of lateral teeth, 

 but more resemble that of .1/. angustatus in tuberculation. The two specimens from 

 Jokkenpiddi agree fairly witli Dana's figure of M. tuberculatum. 



